C18-functionalized Fe3O4/SiO2 magnetic nano-sorbent for PAHs removal from water

Abstract

Magnetic sorbents represent very promising materials for environmental applications due to their simple synthesis, separability in a magnetic field, low toxicity, wide range of possible modifications, and usability in heterogeneous systems. We report on the synthesis, characterization, and application of magnetically separable Fe3O4/SiO2 sorbent surface-modified with octadecyl chains (C18). Preparation of Fe3O4 cores by co-precipitation from Fe2＋ and Fe3＋ chlorides in an alkaline aqueous solution was followed by SiO2 shell synthesis and functionalization with C18. Fe3O4, Fe3O4/SiO2, and Fe3O4/SiO2-C18 samples were characterized by SEM, TOC, XRD, BET, and tested for purification of water contaminated by various polycyclic aromatic hydrocarbons (PAHs). Since PAHs are formed as by-products of pyrolysis, a rapidly evolving technology for transformation of waste into green chemicals, there is a need for efficient sorbents suitable for PAHs removal from the environment. The use of Fe3O4/SiO2-C18 for adsorption of 16 different PAHs has not yet been reported. The adsorption was examined by gas chromatography with mass spectrometry and studied using molecular modeling. Comparison of adsorption efficiency η for Fe3O4, Fe3O4/SiO2, and Fe3O4/SiO2-C18 revealed a positive effect of C18. When averaging all Fe3O4/SiO2-C18 doses tested (1–8 g/L), η > 80% and > 90% was found for 14 and 7 PAHs, respectively, out of a total of 16 tested PAHs. The highest η values were found for medium-heavy PAHs (178.2–228.2 g/mol). Exhibiting high efficiency and average capacity of ∼1μg/g, the Fe3O4/SiO2-C18 is suitable for pre-concentration purposes of PAHs in analytical sample extractions from water.